1. Field of the Invention
The present invention relates generally to downhole tools for use in oil or gas wells, and more particularly, but not by way of limitation, to annulus pressure responsive tools which are electronically controlled in response to command signals transmitted as pressure pulses in the well annulus.
2. Description of the Prior Art
U.S. Pat. No. 4,422,506 to Beck, and assigned to the assignee of the present invention, discloses a typical annulus pressure responsive tester valve of the type utilized by the assignee of the present invention and toward which the modifications of the present invention are generally directed. The Beck apparatus includes a housing having a power piston disposed therein. First and second pressure conducting passages are defined in the housing and communicate the well annulus with first and second sides of the power piston. A metering orifice type of retarding means is disposed in the second pressure conducting passage for providing a time delay in communication of changes in well annulus pressure to the second side of the power piston. Accordingly, a rapid increase or rapid decrease in well annulus pressure causes a temporary pressure differential across the piston which moves the piston. The metering orifice functions to define a temporary reference pressure within the tool which is different from the rapidly changed well annulus pressure so as to provide the necessary pressure differential for operation of the tool.
U.S. Pat. No. 4,711,305 to Ringgenberg, and assigned to the assignee of the present invention, discloses another manner for actuating an annulus pressure responsive downhole tool. The Ringgenberg device utilizes a pressurized gas chamber to provide a compressible fluid spring against which the power piston operates in response to changes in well annulus pressure.
The prior art also includes downhole tools which operate in response to command signals sent from the surface. For example, U.S. Pat. No. 4,347,900 to Barrington; U.S. Pat. No. 4,375,239 to Barrington et al.; and U.S. Pat. No. 4,378,850 to Barrington, all disclose downhole tools operated in response to acoustic command signals transmitted down a pipe string.
U.S. Pat. Nos. 4,796,699; 4,896,722; and 4,915,168, all to Upchurch, all disclose downhole tools responsive to command signals transmitted with a pressure pulse down a well annulus.
There is a need for a simplified means for controlling downhole tools in response to remote command signals.